The present invention falls within the technical sector of mechanics, within the sector of manufacturing transmissions with transmission ratio change, also known as gear boxes.
The object of the present invention is a device that serves as a movement transmission system with continuously variable automatic transmission ratio change. The application of this transmission system is especially applicable to bicycles and other light transport vehicles.
Within the assembly of gear change systems, the invention more specifically falls within the assembly of continuously variable gear change systems. Within the aforementioned sector, the aim of the invention being filed is a transmission system that may automatically and continuously change the transmission ratio thereof, especially suited for use in bicycles.
Today, within the sector for manufacturing transport vehicles, the solution for adapting the speed and torque of the engine device used to the speed and torque used in the wheels or output of the vehicle uses different transmission systems that incorporate systems with changes in the transmission or gear change ratio, in order to adapt the torque of the device to different load and terrain characteristics by means of the different transmission ratios.
On one hand, there are transmissions or gear boxes with a specific number of transmission ratios, the actuation of which may be manual or automatic. We will not deal with this type of transmission since they are substantially different to the type that is proposed and there is no reason to mention some of the many patents filed on said systems.
On the other hand, there are transmission systems with continuously variable transmission ratio between the input and the output. These are desirable for more precise adaptation to different load circumstances and power availability of the system. In addition, they enable maximum variation smoothness between the margins of available transmission ratios.
The aforementioned continuous gear change systems may be used for many types of transport vehicles as an alternative to change systems with a specific number of transmission or speed ratios. Continuous gear changes enable the transmission ratio thereof to change continuously and the ratio variation may be manual or automatic. Specifically for the use thereof in very light transport vehicles, the need to have another type of these continuous transmission ratio change systems, which are economic, simple to use and automatic, is considered.
The transmission system we are concerned with belongs to this group of more specialised transmissions that are of the type with continuous and variable transmission ratio, we will specifically refer to the state of the art of this type of transmission below.
The continuous changes in transmission ratio that are currently known are mainly of the following type:
Those commonly referred to as CVT, where two adjustable opening pulleys are connected via a belt or chain that is adapted to the step variations thereof. This type has been applied to many cars and other vehicles.
Several systems where two discs, one driving and another driven, are connected by an assembly of intermediate elements, the position adjustment of which varies the rolling radii of the connected discs and, therefore, the transmission ratio thereof, the U.S. Pat. No. 6,241,636 by Miller is an example of said systems, and there have been many different designs of these systems with different operating accessories.
Epicyclic gear train systems, where the adjustment of the relative rotation of a planet and sun gear assembly determines the adjustment of the transmission ratio.
Oscillating drive transmission systems, where a back-and-forth push on a lever arm, the shaft of which is connected to a freewheel system, transforms into a continuous rotation, in this system, in order to vary the transmission ratio it is possible to adjust the work distance of the lever arm.
Systems where the connection between the input and output is carried out periodically, using the moments of coincidence of torque requirements.
The U.S. Pat. No. 5,334,115 by Pires describes an oscillating ratchet style transmission.
Unlike the different systems used previously, the present invention focuses on a new automatic and continuous variable transmission ratio change system, which is completely different to the systems that have been used to date, since it is not based on ratio changes in pulleys or gears, or even on the rolling ratio change of two rotating discs connected via spheres or cones that vary their angular position, having in common with the oscillating drive transmissions the fact that the internal operation thereof is discontinuous, the system presented achieves, in a different manner, transmission ratio changes in the rotation between the input and output, by means of the control of the accumulation and exchange of potential and kinetic energy of the system, thereby controlling the transmission ratio between the input and output of the device.
In a manner that is completely different to the changes known to date, the automatic and continuously variable transmission that is described in the present specification, simplified in the operation thereof, uses a rotation input device with the ability to transfer rotation and energy to the input of an elastic potential energy storage unit, which may only release energy by means of the rotation of the output thereof, the rotation of the same being controlled by means of a blocking and release device, which enables the elastic potential energy to be released by means of rotation, in order to transform the elastic potential energy accumulated in the unit into rotation available in the output shaft thereof that is transformed into kinetic energy. By conserving energy between the input and output, the device described in the present specification adjusts the ratio between the input rotation speed and the output of the change to the most optimal depending on the input torque and the output torque requirements.
It is desirable, especially for bicycles, to have a continuously variable transmission available on the market that automatically carries out its transmission ratio variations, thus removing the need to continuously select the gear that is appropriate for the road, and enabling proper driving.
In order to cover this need, the transmission system described in the present specification enables gear boxes of varying complexity to be manufactured, including the simplest for use in bicycles or light vehicles. The aim of the invention is a device conceived to cover a gap in the market in the need described in the state of the art that we have described.